Hormesis

Understanding mechanisms of aging and determinants of life span will help to reduce age-related morbidity and facilitate healthy aging. Average lifespan has increased over the last centuries, as a consequence of medical and environmental factors, but maximal life span remains unchanged. Extension of maximal life span is currently possible in animal models with measures such as genetic manipulations and caloric restriction (CR). CR appears to prolong life by reducing reactive oxygen species (ROS)-mediated oxidative damage.

Redox metabolism has long been considered to play important roles in aging and the development of age-related diseases. Both dietary and pharmacological manipulations of redox metabolism have been associated with the extension of lifespan. Increasing new evidence s also suggests that the process of aging may derive from imperfect clearance of oxidatively damaged material. The accumulation of this molecular "garbage", relatively indigestible, further hinders cellular functions, induces progressive failure of maintenance and repair and increases the probability of death.

The field of toxicology adopted the threshold dose response in the early decades of the 20th century. The model was rapidly incorporated into governmental regulatory assessment procedures and became a central feature of chemical evaluation and assessment. The toxicological community never validated the capacity of this model to make accurate predictions throughout the remainder of the 20th century. A series of recent investigations have demonstrated that the threshold and linear dose response model failed to make accurate predictions in the low dose zone.

SIGNIFICANCE: Among the most highly investigated theories of aging is the mitochondrial theory of aging. The basis of this theory includes a central role for altered or compromised mitochondrial function in the pathophysiologic declines associated with aging. In general, studies in various organisms, including nematodes, rodents, and humans, have largely upheld that aging is associated with mitochondrial dysfunction.

Arsenite is one of the most toxic chemical substances known and is assumed to exert detrimental effects on viability even at lowest concentrations. By contrast and unlike higher concentrations, we here find that exposure to low-dose arsenite promotes growth of cultured mammalian cells. In the nematode C. elegans, low-dose arsenite promotes resistance against thermal and chemical stressors and extends lifespan of this metazoan, whereas higher concentrations reduce longevity. While arsenite causes a transient increase in reactive oxygen species (ROS) levels in C.

Redox metabolism has long been considered to play important roles in aging and the development of age-related diseases. Both dietary and pharmacological manipulations of redox metabolism have been associated with the extension of lifespan. Increasing new evidence s also suggests that the process of aging may derive from imperfect clearance of oxidatively damaged material. The accumulation of this molecular "garbage", relatively indigestible, further hinders cellular functions, induces progressive failure of maintenance and repair and increases the probability of death.

SIGNIFICANCE: Among the most highly investigated theories of aging is the mitochondrial theory of aging. The basis of this theory includes a central role for altered or compromised mitochondrial function in the pathophysiologic declines associated with aging. In general, studies in various organisms, including nematodes, rodents, and humans, have largely upheld that aging is associated with mitochondrial dysfunction.

Hormesis in ageing is probably represented by mild stress-induced stimulation of protective mechanisms in cells and organisms resulting in biologically beneficial effects. Mild stress and hormetins may act on bifurcation points in the complex network of cell signaling and transcription factors, often turning homeodynamics to health or survival. Several signaling pathways activated by diverse stimuli and by stress response converge on NF-?B activation, resulting in a regulatory system characterized by high complexity.

Aging can be viewed as a quasi-programmed phenomenon driven by the overactivation of the nutrient-sensing mTOR gerogene. mTOR-driven aging can be triggered or accelerated by a decline or loss of responsiveness to activation of the energy-sensing protein AMPK, a critical gerosuppressor of mTOR.